http://www.w3.org/Amaya/

Amaya is a Web client that acts both
as a browser and as an authoring
tool. It has been designed with the
primary purpose of being a test bed
for experimenting and demonstrating
new specifications and extensions of
Web protocols and standards. Its
main features include Wysiwyg
editing for HTML documents
including MathML elements, access
to remote documents and publishing
on HTTP servers, support and editing
for Cascading Style Sheets. Note:
This release should be considered a
snapshot of a work in progress. A
large part of the intended features of
Amaya are implemented, but some of
them are not complete yet and the
software is not supposed to be very
robust. The user interface may
change and can be improved.